@Glalie
You do know Blaziken is quite capable of sweeping entire Uber teams easily, yes? In OU the only things that can take it down on equal footing are Talonflame and Azumarill (And they are both wary of switching in if it has Thunder Punch), Chandelure could also take it if it's only running two STAB attacks and it doesn't switch for whatever reason (Since Chandelure is immune to both Fire and Fighting) But that situation is unlikely and Chandelure is rare in OU
As for the rest:
I saw a comment somewhere, can't remember where though, saying that a person got into competative battling this generation hoping for a more balanced metagame. They were disappointed to find that it was just like last generation with everyone running a Blaziken or Genesect
It is a major problem that these Pokemon are so common. That we have to build entire teams around countering them or run a certain Pokemon *CoughTalonflamecough* to beat them. And even then, you can't be certain your opponent isn't running X moveset over Y moveset. That can get your entire team swept
It isn't a matter of "get better at predicting", otherwise people far better than anyone here wouldn't be experiencing these problems as well. Pokemon with such ability and frequency aren't just over used, they're over powered (Ouch, that was a pun...)
Bur that's jsut my opinion, and I can't even really speak from personal experience. I have yet to encounter a Blaziken my Tyranitar can't beat. And have yet to encounter a Genesect at all
And onto Klefki:
I really wouldn't know if it's problematic or not, in Y I usually just Earthquake it with my Hydreigon and it goes down. But from what I gather it's really just annoying, not an actual threat